Marlowe Hood: How Galileo and his spyglass turned the world on its head

Galileo's "optick tube" had a meagre 9x magnification and was not even conceived for astronomy.

Indeed, when the gadget was first demonstrated, Venetian senators were so smitten with its military potential that they doubled Galileo's salary and awarded him a life tenure in the city-state's most prestigious university.

But when, in late October 1609, the 45-year-old Italian mathematician pointed his new-fangled instrument - essentially two lenses aligned in a tube - skyward, what he glimpsed would unleash a scientific revolution and a rare "paradigm shift" in thought.

"He immediately made several surprising discoveries that contributed to the demise of the Earth-centered cosmology that had dominated Western thought for two millennia," says Robert Joseph, a professor of astronomy at the University of Hawaii.

Using ever-more powerful telescopes over the next year, Galileo observed that the Moon was not perfectly smooth, as claimed by Aristotle, but cratered and mountainous.

He spotted hundreds of stars previously untouched by human eyes.

More critically, he discovered the four inner satellites of Jupiter - still known as the "Galilean moons" in his honour - and learnt that Venus, Earth's closest planet, goes through a full range of phases.

Put together, his observations validated the revolutionary theory of Nicolaus Copernicus that Earth orbits the Sun, and not the other way round.

Galileo understood the implications of what he had seen, but the Catholic Church was not ready to accept such heresy.

Only in 2000 did the Holy See apologise for putting Galileo on trial in 1633, forcing him to recant his ideas lest he face imprisonment or worse. The Vatican also pays tribute to him in an exhibition that opened this month...